Grease compositions



Patented Oct. 14, 1952 GREASE COMPOSITIONS Robert J. Moore, Oakland, and Walfrid Saarni, Berkeley, Calif., assignors to Shell Development Company, San Francisco,'Calif., a corporation of Delaware No Drawing. Application September 16, 1949, Serial No. 116,216

13 Claims.

The present invention relates to improvements in greases and, more particularly, to greases having improved mechanical stability.

One of the important characteristics of greases comprises the ability of the composition to maintain its consistency over extended periods of use. This property is particularly important in ball bearing greases and mine loader greases, for example. The ability of a grease to maintain its original consistency can be tested by well known methods which, in brief, comprise working the grease under standardized conditions and periodically determining its penetration. The relatively poor resistance of greases, such as lithium stearate greases, to changes in consistency is well known. A substantial improvement may be made by substituting in whole or in part the fatty acid soap by a soap of a hydroxy fatty acid such as 10 or IZ-hydroxy stearic acid and corresponding acids derived from natural sources such as from hydrogenated castor oil. Where even higher resistance to the adverse influence of continuous Working is desired, even the soaps of hydroxy fatty acids of the character described above are found to be inadequate.

It is an object of the present invention to provide a grease having outstanding mechanical stability. It is another object of the present invention to improve the mechanical stability of greases gelled by the presence of hydroxy fatty acid lithium soaps such as soaps of hydrogenated castor oil fatty acids. It is another object of the present invention to provide a means for improving the mechanical stability of greases comprising lithium 12-hydroxy stearate, especially for use as a ball bearing grease or for a similar utility. Other objects will appear hereinafter.

Now, in accordance with the present invention, it has been found that the mechanical stability of greases thickened with lithium hydroxy fatty acid soap is greatly improved by the addition thereto of a second alkali metal soap, the latter being a soap of a fatty acid having a carbon atom less than 9 carbons removed from the carboXyl group which bears a substituent capable of forming a co-ordinate bond. More particularly, and in accordance with the present invention, the mechanical stability of greases comprising lithium iii-hydroxy stearateis substantially improved by the addition thereto of a minor amount of a lithium hydroxy fatty acid soap wherein the hydroxyl is attached to a carbon atom less than 9 carbons removed from the carboxyl group, or as more particularly described hereinafter.

The stabilizing additives within the purview of the present invention comprise especially metallic soaps of alkane monocarboxylic acids, cycloalkane monocarboxylic acids, and monocyclic aromatic monocarboxylic acids, each of which contains a hydrogen bonding or co-ordinating substituent less than 9 carbon atoms removed from the carboxyl group. The preferred additives which have been found to be especially useful in the present compositions comprise the lithium soaps of alkane hydroXyl monocarboxylic acids, the monocycloalkane hydroxy monocarboxylic acids, and monocycloaromatic hydroxy monocarboxylic acids. Still other preferred grease additives comprise metallic soaps of monoketoalkane monocarboxylic acids and monoaminoalkane monocarboxylic acids wherein the keto or amino groups are attached to carbon atoms less than 9 carbon atoms removed from the carboxylic acid group.

While the lithium soaps are preferred in the present compositions as stabilizing additives, other alkali metals such as sodium and potassium may be employed. The class of compounds having outstanding action in this respect comprises the lithium soaps of monohydroxy alkane monocarboxylic acid having from 3 to 18 carbon atoms wherein the hydroxyl group is in the beta, gammaor delta positions with respect to the carboxyl group such as hydroxy propionic acids, hydroxy butyric acids, hydroxy valeric acids, hydroxy caproic acids, hydroxy enanthic acids, hydroxy caprylic acids, hydroxy lauric acids, hydroxy myristic acids, hydroxy palmitic acids, hydroxy stearic acids, and hydroxy arachidic acids, as-

well as their homologues and analogues.- The corresponding mercapto acids wherein the hydroxy group is replaced by a mercapto group function in a similarly effective manner in the present compositions.

Another effective group of stabilizing agents comprises the monoaminoalkane monocarboxylic acid soaps and especially the lithium soapsof acids such as S-aminopropionic acid, 3-aminohexanoic acid, 3-aminopentanoic acid, a-aminohexanoic acid, S-aminodecanoic acid, as Well as their analogues and homologues. It is preferred that aminoalkane acids having from 8 to 18 'carbon atoms be employed and that substantially unbranched acids are preferred.

Metal soaps of monoketoalkane monocarboicyllcf acidshaving from 3 to 18 carbon atoms may 'be used in the subject greases. These may be 1ithi-- um, sodium, calcium, aluminum or potassium soaps of acids such as pyruvic acid, propionyl 3 carboxylic acid, acetoacetic acid, levulinic acid, and acetobutyric acid. The corresponding thio acids wherein the oxygen atom or the keto group is replaced by a sulfur atom similarly function as stabilizers in the present greases.

A particular type of desirable stabilizer for greases gelled principally by a lithium soap of hydroxy fatty acid comprises metallic soaps of hydroxy naphthenic acids such as those derived from petroleum sources. It will be appreciated that a mixture of this type is more clearly defined by a source than by its exact structure. However, the hydroxy naphthenic acids which are found to be effective in the present compositions are understood to be predominantly hydroxy alkylated cyclopentanoic acids, a large proportion of which comprise hydroxy derivatives of (3-ethyl-d-methyl-1-cyclopentanyl) acetic, butyric and valeric acids. Of course, the pure, clearly defined individual members of this class may be employed if desired. However, the mixture of hydroxy naphthenic acids derived from petroleum oils when saponified with an alkali metal functions as satisfactory stabilizing agents in these compositions.

The soaps of the aromatic acids which function as mechanical stabilizing agents in the present compositions comprise especially those of monocyclic aromatic monocarboxylic acids bearing a hydrogen bonding or co-ordinating substituent such as a nitro, amino, mercapto, hydroxy, keto, sulfo or thiol group attached to the aromatic ring or to a short side chain thereon. Typical soaps of this description include the sodium, potassium, aluminum, calcium or lithium soaps of ortho-, meta-, or para-nitrobenzoic acid; ortho-, meta-, or para-aminobenzoic acid; ortho-, meta-, or para-thiolbenzoic acid; ortho-, meta, or parahydroxybenzoic acid; mandelic acid, tropic acid, benzoyl formic acid and benzoyl acetic acid.

The soaps which function as outstanding stabi lizers in the present compositions include those such as described above, especially those of the substituted alkane acids having substantially no branching in the hydrocarbon portion of the molecule as well as the cyclo-alkane or aromatic acids bearing a minimum of branched chain substituents. The examples appearing hereinafter indicate that the position of the hydrogen bonding or co-ordinating substituent with respect to the carboxyl group is immaterial as long as it is dependent from a carbon atom less than 9 carbon atoms removed from the carboxyl group. If a greater space exists between the two functional groups, the enhanced mechanical stability of the grease correspondingly suffers.

The principal gelling agents in the greases under consideration comprise lithium soaps of hydroxy fatty acids wherein the hydroxyl group is in a position more than 9 carbon atoms removed from the carboxyl group. Typical soaps of this character have been described in numerous references. The preferred soap of this character is the lithium soap of l2-hydroxy stearic acid or the corresponding acids derived from hydrogenated castor oil. The grease may contain in addition to the lithium soap of a hydroxy fatty acid an alkali metal soap of a higher fatty acid such as sodium stearate or oleate or a calcium soap of a higher fatty acid or a lithium soap of a higher fatty acid. In producing the lithium soap of a hydrogenated castor oil or of the fatty acids derived therefrom, any suitable lithium compound may be used including lithium hydrate, lithium carbonate, lithium oxide and the like. Preferably, due to availability and ease of manufacture, the lithium compound used is lithium monohydrate which contains from 53 to 55% of lithium hydroxide. The soaps are preferably formed in the presence of at least a portion of the lubricating oil ingredient of the grease, as more particularly described hereinafter. Soaps of hydrogenated ricinoleic acid also may comprise the principal gelling agent present in the grease.

The lubricant comprising the base of the grease will, in most cases, be a mineral lubricating oil. However, natural oils such as vegetable oils or animal oils maybe employed as well as synthetic lubricants such as polymerized olefins, polyalkylene oxides such as polypropylene oxide, polymerized sulfides such as poly-propylene sulfide, polymerized glycols such as polyethylene glycol, esters of dicarboxylic acids such as bis-(2- ethylhexyl) sebacate and phosphates such as tributyl phosphate or tricresyl phosphate. In cases where high temperature use is contemplated, the silicones may be used in whole or in part.

The respective quantities of each of the three principal ingredients may be varied within relatively wide limits to suit particular applications. The stabilizing additives such as those described above which constitute 0.01 to 1% by weight of the total grease composition are preferably present in from about 5 mole per cent to about 10 mole per cent of the total soap content and preferably from about 6 mole per cent to 8 mole per cent thereof. Within this preferred range, the increase in mechanical stability is far greater than in the broader range recited. It is preferred that the proportion of stabilizing soap be below 8% since beyond this figure the penetration of the composition increases sharply. Maximum results are obtained when approximately 7 mole per cent of the total soap content comprises the soap of the stabilizing acids described above.

The total soap content of the greases may be from about 3% to 40% by weight of the total grease; preferably the soap content is between 6% and 15% by weight of the grease. It will be understood that mixtures of the three principal components may be employed. For example, when a low temperature grease is required, up to about 20% by weight of the oil component is desirably an ester of a dicarboxylic acid such as bis-(2-ethylhexyl) sebacate. Mixtures of either pure or natural soaps for both the principal gelling agent and for the stabilizer may be used. Other ingredients which may be present in the compositions comprise glycols such as glycerine, for the prevention of bleeding and the like, and anti-oxidants such as para-phenylene diamine. In many instances, additives of this type are found to be unnecessary since the described classes of stabilizing soaps have been found to improve not only the mechanical stability of the grease compositions but also its resistance to bleeding and oxidation.

The preparation of the subject greases preferably follows the process earlier described in prior art patents. A typical preparation of lithium greases comprises saponification of the two classes of carboxylic acids, namely, the major grease forming hydroxy fatty acid and the stabilizing acid, dehydration of the soap in the presence of a portion of the oil, solution of the soap in oil by heating and precipitation of the soap in the desired fiber form by lowering the temperature, preferably together with stirring and working. More particularly, it has been found that greases having the optimum consistency are prepared by mixing the two types ofacids with about of the oil, adding lithium hydrate at about 100 0., raising the temperature to about 200. C. but not over 210 C. in order to dehydrate the concentrated soap mixture and to dissolve the soap in the oil, quenching the concentrat-e by the addition of the remaining portion of the oil to a temperature of about 165 C., reheating the entire mixture to about 190 C. and finally cooling to room temperature while working the grease. While preformed soaps may be added to the oil, it has been found that the procedure as described above results in the formationof greases having optimum consistency and bleeding properties as well as stability. It should be emphasized that excessive preparation temperatures should be avoided and particularly temperatures above about 210 C. It is well known that decomposition of hydroxy acids begins-at about 200 C. and proceeds rapidly at higher temperatures so that the small amounts of added promoter may be destroyed by heating at substantially above 210 C. Thus, sodium lactate-yields acrylates, as well as other decomposition products. Similarly, the other substituted acids referred to tend to decompose at elevated temperatures and they are then no longer effective.

The function of the stabilizing soap which is present in minor proportion has not been definitely ascertained, but probably the major reason for the stabilizing action is the additional bonding in the soap crystal due to the co-ordinate bonding of the co-crystallized stabilizing soap contributin to crystal strength so that the rate of gel break-down with working is retarded. This additional bonding may be either intercrystalline or intra-crystallite. While the invention is not to be limited by any postulated theories, these may be employed in studying the basic phenomena which occur in the present instance.

The mechanical stability of the greases produced in accordance with the present invention may be tested with the Shell Roll tester currently used extensively in the grease industry. The apparatus in which the test is made is a simulated roller bearing and consists of a horizontal 3 inch hollow cylinder, seven inches long, into which there is placed a solid steel cylinder 2% inches in diameter and about seven inches long, weighing approximately 11 pounds. The larger cylinder, initially closed at one end, has a cap placed over the open end after the grease has been introduced. Enough clearance is permitted for the solid steel cylinder to roll freely inside the larger cylinder which is rotated at 160 R. P. M., and the solid cylinder rotates by means of contact with the inside of the larger hollow cylinder. In an apparatus of this character, a given amount of grease may be rolled for a period of time and tested for consistency to obtain the degree of mechanical stability of the grease. The smaller cylinder rolls, works and masticates the grease thoroughly during the test.

At given time intervals, the grease is removed, tested for consistency and then replaced in the apparatus for further working. The consistency of the grease is determined by means of a special small cone attached to the regular ASTM penetrometer. A small cup is used in conjunction with the test. The worked penetration obtained by this apparatus is referred to herein as micro penetration which may be correlated, if desired, with the regular ASTM penetration by means of apreviouslydetermined curve. The roll stability of a grease comprises the time required for rolling in the above apparatus for the grease to reach a maximum micro penetration of 230 dmm. It will be recognized by experts in the art that the greasesdescribedmay be modified by the inclusion, of anti-oxidants, anti-bleeding agents, mixed lubricants, mixed soaps, and other technical variations for specific purposes.

A turbine mineral oil lubricant was used as the base lubricant in the present tests. One-third of the oil was mixed with'hydrogenated castor oil or with a mixture of said glyceride and stabilizing acids in proportions to yield a final grease having a total of 6% lithium soaps containing 0.25% byweight (except as noted) of the stabilizing soaps. At C., lithium hydrate was added to saponify the glyceride and the stabilizing acid and the concentrated soap slurry was heated to 200 C. to dissolve the soaps in-the oil and dehydrate the composition. The remaining portionof the lubricating oil was added to quench the composition after which it was reheated to C. and subsequently cooled with stirring. The resulting grease was tested in'the roll tester described above and removed periodically for determination of micro penetration. The examples which follow illustrate the roll stability, in hours, of greases containing non of the stabilizing additives as compared with greases containing a wide variety of such additives.

Table Roll Additive (Lithium soap) Stability,

Hours None 100 Lactic acid (0.1%) 500 Alpha-hydroxy stearic acid 400 Beta-hydroxy propionic acid (0.1%) 270 Gamma-hydroxy valeric acid (0.1%) l000 Delta-hydroxy valeric acid (0.1%) 440 (i-Aminocaproic acid 300 4-Ketovaleric acid (0.1%) 500 Ortho-hydroxy benzoic ac 240 Meta-hydroxy benzoic acid 200 Mandelic acid 1 280 Ortho-nitrobenzoic acids. 350 Ortho-aminohenzoic acid. 400 Oxidized hydrocarbon aci 350 Petrolcum'hydroxy naphthenic a 190 The specificity of polar substituted carboxylic acids for stabilization of the grease structure can be shown by comparison with representative nonsubstituted acids which do not promote mechanical stability; caprylic acid, benzoic acid, dodecyl benzoic acid, stearic acid, etc. It has also been found that substituted hydrocarbons which do not form metal salts, such as B-naphthol, benzophenone, etc donot enhance the mechanical stability of these greases.

We claim as'our invention:

1. -A grease composition comprising a mineral lubricating oil and having incorporated therein in an amount to thicken the mineral oil to a grease consistency a lithium soap of a high molecular weight hydroxy fatty acid wherein the hydroxyl' group is more than 9 carbon atoms removed from the carboxyl group and 0.01 to 1.0% by weight of a lithium soap of gamma-hydroxy valeric acid. T

2. A grease composition comprising a mineral lubricating oil and having incorporated therein in an amount to thicken the mineral oil to a grease consistency a lithium soap of a high molecular Weight hydroxy fatty acid and 0.01 to 1.0% by weight of a lithium soap of delta-aminocaproic'acidl l i 3. A ,greaserco'mpositidn comprising. a mineral lubricating oil and having incorporated therein in an amount tothicken the mineral oil to a grease consistency a lithium soap of a high molecular weight hydroxy fatty acid wherein the hydroxyl group is more than 9 carbon atoms removed from the carboxyl group and 0.01 to 1.0% by weight of a lithium soap of '4-ketovaleric acid.

4. A grease composition comprising a mineral lubricating oil and having incorporated therein in an amount to thicken the mineral oil to a grease consistency a lithium soap of a high molecular weight monohydroxy fatty acid wherein the hydroxyl group is more than 9 carbon atoms removed from the carboxyl group and 0.01 to 1.0% of a second alkali metal soap of a hydroxy fatty acid having 3 to 18 carbon atoms wherein the hydroxyl group is less than 9 carbon atoms removed from the carboxyl group.

5. A grease composition comprising a mineral lubricating oil and having incorporated therein in an amount to thicken the mineral oil to a grease consistency a lithium soap of a high molecular weight monohydroXy-fatty acid wherein the hydroxyl group is more than 9 carbon atoms removed from the carboxyl group and 0.01 to 1.0% of a second alkali metal soap of an aromatic monohydroxy monocarboxylic acid wherein the hydroxyl group is less than 9 carbon atoms from the carboxyl group.

6. A grease composition comprising a mineral lubricating oil and having incorporated therein in an amount to thicken the mineral oil to a grease consistency a lithium soap of a high molecular weight monohydroxy fatty acid wherein the hydroxyl group is more than 9 carbon atoms removed from the carboxyl group and 0.01 to 1.0% of a second alkali metal soap of a cycloaliphatic monohydroxy monocarboxylic acid wherein the hydroxy group is less than 9 carbon atoms from the carboxyl group.

7. The method of increasing the shear stability of a grease, comprising a lubricating oil and a lithium soap of a hydroxy fatty acid wherein the hydroxyl group is more than'9 carbon atoms removed from the carboxyl group in an amount sufiicient to thicken the oil to a grease consistency which comprises incorporating in the grease 0.01 to 1.0% by weight of a second alkali metal soap of a monohydroxy monocarboxylic acid having 3 to 18 carbon atoms, wherein the hydroxyl group is less than 9 carbon atoms from the carboxyl group.

8. The method of preparing a shear stable grease comprising commingling the lithium soap of l2-hydroxy stearic acid and a lubricating oil in amounts sufficient to thicken the oil toa grease consistency, together with 0.01 to 1.0% by weight of a second lithium soap of a monohydroxy monocarboxylic acidhaving 3 to 18 carbon atoms,

wherein the hydroxyl group is less than 9 carbon.

atoms from the carboxyl group, heating saidmixture to dissolve the soaps, but not in excess of about 210 C., and cooling the soap-oil mixture to re-precipitate the soap in a fibrous form of en.- hanced mechanical stability.

9. A grease composition comprising a lubricating oil base and a lithium soap of a hydroxy fatty acid having 10 to 24 carbon atoms, wherein the hydroxyl group is more than 9 carbon atoms removed from the carboxyl group, in an amount sufficient to thicken said oil to a grease consistency, and a second alkali metal soap ofan organic monocarboxylic acid having 3 to 18 carbon atoms, said, secondv soap bearing a. substituent which is capable of forming a coordinate bond and which is less than 9 carbon atoms removed from said carboxyl group, the second soap being present in an amount between 0.1 and 0.25% by weight of the grease composition, the substituent being one selected from the group consisting of hydroxy, keto, amino, nitro, mercapto, thiol and sulfo groups.

10. A process for improving the mechanical stability of a grease gelled with a lithium soap of a hydroxy fatty acid having from 10 to 24 carbon atoms, wherein said hydroxy group is more than 9 carbon atoms removed from a carboxyl group, which comprises adding to said grease between 0.1% and 0.25% by weight based on the final composition of a second alkali metal soap of an organic monocarboxylio acid having 3 to 18 carbon atoms and having a substituent which is capable of forming a coordinate bond and which is less than 9 carbon atoms removed from said carboxylic group, said substituent being selected from the group consisting of hydroxy, keto, amino, nitro, mercapto, thiol and sulfo groups and heating the composition containing said soap to a temperature not exceeding 210 C.

11. A grease composition comprising a lubricating oil base and containing a lithium soap of a hydroxy fa ty acid having 10 to 24 carbon atoms per molecule wherein the hydroxyl group is more than 9 carbon atoms removed from the carboxyl group and a second alkali metal soap of a monohydroxy monocarbcxylic acid having 3 to 18 carbon atoms per molecule wherein the hydroxyl group is less than 9 carbon atoms from the carboxyl group, the first soap being present in an amount sufficient to thicken the oil to a grease consistency and the second soap being present in an amount between 0.01% and 1% by weight of the grease composition, the amount of said second soap being sufficient to improve substantially the shear stability of said grease.

12. A grease composition comprising a lubrica ing oil base and containing a lithium soap of a hydroxy fatty acid having 10 to 24 carbon atoms per molecule wherein the hydroxyl group is more than 9 carbon atoms removed from the carboxyl group, said soap being present in an amount sufiicient to thicken the oil to a grease consistency, and a second alkali metal soap of an organic monocarboxylic acid having 3-18 carbon atoms per molecule and bearing a substituent capable of forming a coordinate bond less than 9 carbon atoms removed from the carboxyl group, said substituent being selected from the group consisting of hydroxy, keto, amino, nitro, mercapto, thiol and sulfo groups, the second soap being present in an amount between 0.01% and 1% by weight of the grease, said amount being suflicient to improve substantially the mechanical stability of the grease.

13. A grease composition comprising a mineral lubricating oil base and containing a lithium soap of a hydroxy fatty acid having 10-24 carbon atoms per molecule wherein the hydroxy radical is more than 9 carbon atoms removed from the carboxyl group, said soap being present in an amount suflicient to thicken the oil to a grease consistency and a second lithium soap of an organic monocarboxylic acid having 3-18 carbon atoms per molecule and bearing a substituent capable of forming a coordinate bond less than 9 carbon atoms removed from the carboxyl group, said substituent being selected from the group consisting of hydroxy, keto, amino, nitro, mercanto, thiol and suuo' joubs. the second sqiap REFERENCES crmn being Present m an me nfl 091% a The following references are or reebm m the 1% by weight of the g rease end in such propor me or this Patent: 7 tion as to constitute ir'omflabout 5 mole percent; to about 10 mole percentlof the total soap cdnqw UNITED STATES PAWS tent and sumcient tojimprdve substantially ,the; Number Name Dye mechanical stability 01 the grease. 2,182,137 Ricketts 0"]5, 1939 I 2,340,438 Strawn "fEeb-.-;g-1, 1944 ROBERT J. MOORE. 2,397,956 Fraser Ap 9, 1946 qwmm SAARNI. 10 2,450,254 Puryear et a1 se t.=za. 1943 2,468,098 Morway et a1 ..-'Apr. '6, 1949 2,487,030 Swenson ei. 1949 

9. A GREASE COMPOSITION COMPRISING A LUBRICATING OIL BASE AND A LITHIUM SOAP OF A HYDROXY FATTY ACID HAVING 10 TO 24 CARBON ATOMS WHEREIN THE HYDROXYL GROUP IS MORE THAN 9 CARBON ATOMS REMOVED FROM THE CARBOXYL GROUP, IN AN AMOUNT SUFFICIENT TO THICKEN SAID OIL TO A GREASE CONSISTENCY, AND A SECOND ALKALI METAL SOAP OF AN ORGANIC MONOCARBOXYLIC ACID HAVING 3 TO 18 CARBON ATOMS, SAID SECOND SOAP BEARING A SUBSTITUENT WHICH IS CAPABLE OF FORMING A COORDINATE BOND AND WHICH IS LESS THAN 9 CARBON ATOMS REMOVED FROM SAID CARBOXYL GROUP, THE SECOND SOAP BEING PRESENT IN AN AMOUNT BETWEEN 0.1% AND 0.25% BY WEIGHT OF THE GREASE COMPOSITION, THE SUBSTITUENT BEING ONE SELECTED FROM THE GROUP CONSISTING OF HYDROXY, KETO, AMINO, NITRO, MERCAPTO, THIOL AND SULFO GROUPS. 